- Email: [email protected]
Purification of landfill leachate with reverse osmosis and nanofiltration
DESALINATION ELSEVIER
Desalination 119 (1998) 289-293
Purification of landfill leachate with reverse osmosis and nanofiltration Thomas A. Peters Dr.-lng. Peters Consultingfor Membrane Technology and Environmental Engineering Broichstr. 91, 41462 Neuss, Germany Tel: ÷49(2131)228963; Fax: +49(2131)545040; email: [email protected] Received27 June 1998
Abstract On many landfill sites the most environmentally friendly and economical way to treat landfill leaehate is to reduce its volume by 75 to 80% using reverse osmosis and then return the concentrate to the landfill by controlled reinjeetion. If this procedure is not yet authorized by local authorities then the treatment process must achieve very high rates of recovery by using a combination of reverse osmosis and nanofiltration technology with controlled crystallization to reduce the volume of concentrate for further processing.
Keywords: Reverse osmosis; High pressure reverse osmosis; Nanofiltration; Landfill leachate; Reinjection; Solidification
1. Components dissolved in leachate An evaluation o f the data for the leachate from more than 150 landfills in Germany [1] and from few in Spain [2] shows, that the amount o f components dissolved in leachate from different kind o f landfills covers the rangefrom 2 to 15 g/l. From this the fraction o f or-
ganic components is considered to cover a range between 0.1 and 3 g/l. That is much smaller than the inorganic part, indicated to have a range from 1.6 to 14.3 g/l, including ammonia with values between 0.3 to 2 g/l. This between 80 and 95% o f the components dissolved in landfill leachate correspond to inorganic material and only between 5 and 20% are o f organic origin.
Presented at the Conferenceon Membranes in Drinking and Industrial Water Production, Amsterdam, September21-24, 1998,, International Water Services Association, European Desalination Society and American Water Works Association 0011-9164/98/$ - See front matter © 1998 Elsevier SeieneeB.V. All rights reserved. P// S0011-9164(98)00171-4
290
T.A. Peters ~Desalination 119 (1998) 289-293
Since such contaminants are mostly not appropriate for trealment by conventional biological processes new regulations tend to limit the discharge of such complex wastes to municipal sewers. Even by combining biological treatment with adsorption by active carbon or with the oxidation of part of the dissolved organic material using ozone or other oxidizing agents, only partial destruction of contaminants will be achieved. It will not reach the purification needed to fully reduce the negative impact of landfill leachate on the environment [3]. One aspect is the so called "hard COD" that is not biodegradable and cannot be destroyed or adsorbed and thus will remain in the water discharged after being treated with the mentioned processes, causing problems in the future as a consequence of the effects of long time accumulation. Therefore more effective methods of treatment of this material have had to be developed. The use of reverse osmosis either as a main step in a landfill leachate treatment chain or as single step has shown to be a very successful means of achieving full pmification. 2. Reverse osmosis for the purification of landfill leaehate Due to the ability of modem high-rejection reverse osmosis membranes to retain both organic and inorganic contaminants dissolved in water at rejection rates of 98-99%, reverse osmosis is also useful for purifying liquid waste such as landfill leachate and for helping to solve the growing problem of water pollution. Thepermeate contains only very low levels of inorganic and organic contaminants. These meet potable water standards and discharge of this water to the next river or aquifer contributes to maintenance of the natural equilibrium as this leachate was originally mainly clean rain water. As the reverse osmosis membrane is operating like a well defined barrier the purification
process itself can be controlled continuously and with a high degree of security by the simple and precise measurement of the electric conductivity. Because of the high rejection rate for each kind of contaminant dissolved in the feed water a high flexibility against changes of the concenttafon of the compounds in landfill leachate is given. Therefore the permeate produced has always the expected high quality, as this is based on a reproducible high purification efficiency. However in addition to requiring highly resistant membranes, the treatment of landfill leachate with reverse osmosis demands the use of open channel module systems that can be cleaned with high efficiency with regard to scaling, fouling and especially biofouling. Therefore tubular modules were the first medium used in the early reverse osmosis systems for the purification of landfill leachate starting in 1984. An alternative was inlroduced to this market in 1988. The disc-tube-module (DTmodule) has been installed since then with great success [4]. By the year 1997, plants equipped with this DT-module represented more than 80% of the total capacity installed for the purification of landfill leachate by reverse osmosis. The successful operation of reverse osmosis in the plant of the municipal waste landfill of lhlenberg (former VEB Deponie Sch6nberg) near the city of Ltibeck in Germany, the most modem and largest multi-stage plant that has been realized up to this time for landfill leachate purification, demonstrates the possibilities of modem membrane technology. Some results are given as example in Table 1. This reverse osmosis system with a capacity of 36 m3/h has been in operation without any problem since the 15th of December of 1989 with one change of the membranes till now. With two reverse osmosis stages, the average rejection rates for salts and organic contaminants are about 99°,6. Depending on the salt content of the feed water and the operation time
T.A. Peters./Desalination 119 (1998) 289-293
between the cleaning cycles, the operating pressure ranges between 36 and 60 bar at ambient temperature. The specific p¢cmeate flux was calculated to be approximately 15 l]m 2 h. Table 1 Typicalplantperformancein leachatepurification Parameter pH-value El. conduct., ~S/em COD, mgO-/l Ammonium, mg/l Chloride,mg/l Sodium, mg/l Heavymetals, mg/l
Ix,achatePermeate 1Permeate2 Rejection, % 7.7 6.8 6.6 17,250 382
20
99.9
1,797
15
<15
>99.2
366
9.8
0.66
99.9
2,830 48.4 1.9 4,180 55.9 2.5 0.25 <0.005 <0.005
99.9 99.9 >98
Similar results are reported from other plants, for example from the landfill Kolenfeld near Hannover, with start up in February 1990. This plant, operated with 1.8 mS/h, has an availability of over 90%. The electric conductivity of the feed is reported to be 15,000 to 16,000 ttS/em, the rejection rate always more than 98%, for COD 99%o. New membranes were installed in April 1993, after more than 3 years in operation because of a decreasing permeate flux. These data from long term experience have also been confirmed by the results of the other more than 120 systems that are in operation on different landfills up to now and by the data collected during numerous tests with pilot plants in technical scale all over Europe, North America and in some countries in Far East. 3. Handling o f ieachate concentrate
The purification of landfill leachate helps to avoid further contamination of the resources like groundwater and surface water. But beside the ecological aspect---the minimization of the burden on the environment~also has to be taken
291
into consideration the commercial feasibility, i.e. the affordability. In this regard membrane filtration has proved to be a justifiable and economic solution in most of the cases, even when the overall costs for the purification are compared with other approaches for the treatment of landfill leachate. This evaluation includes the handling of the concentrate produced in the reverse osmosis plants with 75 to 80% recovery rate, that in the past has been considered to be a very cost intensive step. That applies in fact for few plants in operation, that are using evaporation and drying followed by deposition of the dry residues in a special landfill. However, today other possibilities are gaining importance. They have been developed considering the best technology available and at the same lime ecological and economical requirements. These are: a) transport of the concentrate to an incineration plant equipped for the burning of liquid hazardous waste; b) the solidification of the concentrate with different materials, like fly ash [5] or sludges from waste water treatment plants [6], and disposal of this kind of dry residue on the landfill itself; c) controlled reinjection of the concentrate into changing areas of the landfill in order to improve the biochemical degradation process in the waste itself and accelerate the immobilisation of the organic matter. This solution should be considered as first approach, as a landfill usually can be compared to a bioreaetor that under optimal operating conditions will produce valuable landfall gas, in this case accelerating at the same time the desired imrnobilisation of organic components [7]. If the system for the controlled return of the concentrate to the landfill is designed according to the needs and the respective conditions on site no changes for the concentration of poUutants in the leaehate being pumped from the landfill to the purification plants are to be ex-
292
T.A. Peters ~Desalination 119 (1998) 289-293
peeted. This has been demonstrated on different landfills, in one case since 1986 [1,8,9]. Nevertheless the decision about the concentration factor of a leachate purification system should be based on eval~.~_afioncriteria that include all kind of economical and ecological aspects specific for each landfill site in order to find an op"tmaized solution. In some cases a one stage unit could be sufficient, in others a combination of processes with the highest possible recovery rate should be selected. 4. Volume reduction for the concentrate
Steady improvement of membrane technology has resulted in a high pressure reverse osmosis system based on the DT-module with operation pressures in the range of 120 bar and an adapted process to reduce certain salt fiactions by controlled precipitation. With these developments, the limits for the recovery rate in landfill leachate---given among others by the osmotic pressuro---have been overcome and the concentration factor for the organic and inorganic matter dissolved in the landfill leachate was doubled. This means an increase of the permeate recovery from about 80%--- related to a concentration factor of 5--to 90% recovery with a concentration factor of 10 for the contaminants retained by the membrane. Thus the limit for the electric conductivity in the concentrate of a reverse osmosis plant was increased from 50,000 to 60,000 ~tS/crn to the range of 100,000 to 120,000 ~tS/em [4]. Due to the high volume reduction related to this increase of pure water recovery, this technology allows the need for subsequent evaporation steps to be eliminated. After being processed with high pressure reverse osmosis, the concentrate can then be fed directly into a dryer or a solidification device, or be burned. Such high pressure reverse osmosis systems are in use actually at about 25 plants. On the Ihlenberg landfill site high pressure reverse osmosis has been working since January
1992 with a salt rejection of more than 99%, for example from 73,280 ~tS/cm in the feed to 434 pS/cm in the permeate. The average specific energy demand for this concentrate stage is 14 kWh/m3 permeate, whereas the leachate stage with 80% recovery in fi'ont of this system is consuming less than 5 kWh/m3. The continuous growth of this landfill and the accompanying increase in leachate required the expansion of the purification capacity. On December 17, 1993 the next reverse osmosis plant was brought on line with an integrated high-pressure stage (manufacturer PALL ROCHEM) that increased the input capacity to another 48 m3/h of raw leachate [5], being possible under favourable conditions a permeate recovery up to 90%. 5. Process improvement with nanofiitration
Even better permeate recovery rates can be reached by installing a combination of nanofiltration and fractionated removal of solids together with reverse osmosis and high pressure reverse osmosis. Nanofiltration allows material dissolved in water to be separated into monovalent and bivalent ions. Consequently, the high rejection rate for sulphate ions and for dissolved organic matter together with very low rejection for chloride and sodium reduces the volume of concentrate. Some example for rejection rates for different components dissolved in landfill leachate are shown in Table 2 [10]. For this application, very specific nanofiltration membranes have to be selected and the module must be suitably designed to optimize the interaction of flow parameters such as feed flow velocity, pressure drop, efficient membrane cleaning, insensitivity to micro-particles. Also, a good cost/performance ratio must be achieved. These requirements for successful and continuous separation of heavily loaded waste water are met by the DTF-module, a flat channel module consisting of only a few components in which open-channel construction is combined with narrow gap technique.
T.A. Peters. ~Desalination 119 (1998) 289-293 Table 2 Example for rejection rates for nanofiltration Parameter BODs, mg 02/1 COD, nag 02/1 Ammonia,
Feed 480
Pernm~ 280
P,.ejoction,% 41.62
17000 3350
700 1420
95.88 57.61
31200 12760 2670 1030 10900 6.3 61
2345 17730 187 72.7 5010 6.4 43
92.48 -38.95 93.00 92.94 54.04 -29.5
mg/l Sulphate, mg/l Chloride, mg/l Calcium, mg/l Magnesium, rag/1 Sodium, mg/l pH-value El. conduct., ~tS/em
A system operated with 8.5 kWh/m3 of totally produced permeate with a water recovery rate o f 97% is one example for the extremely low overall power consumption of this hybrid process using reverse osmosis, nanofiltration and fraetionated removal of solids. The fact that a permeate recovery rate o f 95 to 97.5% is operating standard today shows that the combination o f reverse osmosis with nanofiltration and crystalliTation is the basis for a economical process for the purification o f landfill lcachate. Based on the technology explained above, companies have introduced an "own and operate" service, where clients simply pay a price per m 3 of leachate treated without capital risk and with minimal operational involvement. Also it is possible to operate equipment for short term emergency situations, caused by heavy precipitation and capacity bottle-necks.
6. Conclusions
The results obtained during the operation of an increasing number of plants under very different conditions prove that reverse osmosis is a
293
very effective msmtment for the purification o f landfill leachate if all design criteria and requirements specific for landfill leachate have been taken into consideration, and i f an adapted module system as well as correlated technologies are used. This includes high pressure reverse osmosis, with operating pressure up to 120 bar and/or nanofdtration in combination with a controlled crystallization process, that allows permeate recovery rates of more than 95%. The elimination of the negative impact of landfill leachate on the environment can be achieved with membrane filtration due to the dramatic minimization of residual waste to beprocessed or immobilized and due to the high quality of the purified water discharged back to nature. The combination of processes designed for this purpose is one example for a sustainable environmentally friendly development. References [ 1]
W. Dahm J.S. Kollbaeh and J. Gebel, Sickerwass~Roinigung - Stand dcr Tochnik 1993/94 - zxfla?mfligc Entwiddunge~ EF-Verlag fla" Energie- und Umwelttechnik GmbH, Berlin, 1994 [2] AMASA, Archives, Ban:elona, 1998 [3] T. Peters, Water Qualityintemational, 9-10 (1996) 23. [4] T. Peters, Prec., Sardinia 95, 5th International Land-
fill Symposium,~ A , S. Margheritadi Pula- Cagli~Jtaly,.,1995. [5] R.Kenner1L and T. Peters,WLB Wasser, LuRund Boden 1-2 (1995) 24. [6]
M. Raphtel, W. Pohl and T. Peters, Lecture abstracts, ACHEMA 1994, Frankfurt. [7] F. Pohland~ Water Quality International, 9-10 (1996) 18. [8} G. Gross¢ G, DcponiesickorwasseramOocmitung bis zur Direkteinleitung und Totalcntsorgung, TAW, 30./31.01.1990, Ostfildcm. [9] P.L.A. Hcnigin, Prec., Sardinia 95, 5th International Landfill Symposium, CISA, 1995; S. Margherita di Pula - Cagliari, Italy, 1995. [10] R. Rautenbach R. and T. Linn, Entsorgungspraxis, 9 (1995) 44.
Desalination 119 (1998) 289-293
Purification of landfill leachate with reverse osmosis and nanofiltration Thomas A. Peters Dr.-lng. Peters Consultingfor Membrane Technology and Environmental Engineering Broichstr. 91, 41462 Neuss, Germany Tel: ÷49(2131)228963; Fax: +49(2131)545040; email: [email protected] Received27 June 1998
Abstract On many landfill sites the most environmentally friendly and economical way to treat landfill leaehate is to reduce its volume by 75 to 80% using reverse osmosis and then return the concentrate to the landfill by controlled reinjeetion. If this procedure is not yet authorized by local authorities then the treatment process must achieve very high rates of recovery by using a combination of reverse osmosis and nanofiltration technology with controlled crystallization to reduce the volume of concentrate for further processing.
Keywords: Reverse osmosis; High pressure reverse osmosis; Nanofiltration; Landfill leachate; Reinjection; Solidification
1. Components dissolved in leachate An evaluation o f the data for the leachate from more than 150 landfills in Germany [1] and from few in Spain [2] shows, that the amount o f components dissolved in leachate from different kind o f landfills covers the rangefrom 2 to 15 g/l. From this the fraction o f or-
ganic components is considered to cover a range between 0.1 and 3 g/l. That is much smaller than the inorganic part, indicated to have a range from 1.6 to 14.3 g/l, including ammonia with values between 0.3 to 2 g/l. This between 80 and 95% o f the components dissolved in landfill leachate correspond to inorganic material and only between 5 and 20% are o f organic origin.
Presented at the Conferenceon Membranes in Drinking and Industrial Water Production, Amsterdam, September21-24, 1998,, International Water Services Association, European Desalination Society and American Water Works Association 0011-9164/98/$ - See front matter © 1998 Elsevier SeieneeB.V. All rights reserved. P// S0011-9164(98)00171-4
290
T.A. Peters ~Desalination 119 (1998) 289-293
Since such contaminants are mostly not appropriate for trealment by conventional biological processes new regulations tend to limit the discharge of such complex wastes to municipal sewers. Even by combining biological treatment with adsorption by active carbon or with the oxidation of part of the dissolved organic material using ozone or other oxidizing agents, only partial destruction of contaminants will be achieved. It will not reach the purification needed to fully reduce the negative impact of landfill leachate on the environment [3]. One aspect is the so called "hard COD" that is not biodegradable and cannot be destroyed or adsorbed and thus will remain in the water discharged after being treated with the mentioned processes, causing problems in the future as a consequence of the effects of long time accumulation. Therefore more effective methods of treatment of this material have had to be developed. The use of reverse osmosis either as a main step in a landfill leachate treatment chain or as single step has shown to be a very successful means of achieving full pmification. 2. Reverse osmosis for the purification of landfill leaehate Due to the ability of modem high-rejection reverse osmosis membranes to retain both organic and inorganic contaminants dissolved in water at rejection rates of 98-99%, reverse osmosis is also useful for purifying liquid waste such as landfill leachate and for helping to solve the growing problem of water pollution. Thepermeate contains only very low levels of inorganic and organic contaminants. These meet potable water standards and discharge of this water to the next river or aquifer contributes to maintenance of the natural equilibrium as this leachate was originally mainly clean rain water. As the reverse osmosis membrane is operating like a well defined barrier the purification
process itself can be controlled continuously and with a high degree of security by the simple and precise measurement of the electric conductivity. Because of the high rejection rate for each kind of contaminant dissolved in the feed water a high flexibility against changes of the concenttafon of the compounds in landfill leachate is given. Therefore the permeate produced has always the expected high quality, as this is based on a reproducible high purification efficiency. However in addition to requiring highly resistant membranes, the treatment of landfill leachate with reverse osmosis demands the use of open channel module systems that can be cleaned with high efficiency with regard to scaling, fouling and especially biofouling. Therefore tubular modules were the first medium used in the early reverse osmosis systems for the purification of landfill leachate starting in 1984. An alternative was inlroduced to this market in 1988. The disc-tube-module (DTmodule) has been installed since then with great success [4]. By the year 1997, plants equipped with this DT-module represented more than 80% of the total capacity installed for the purification of landfill leachate by reverse osmosis. The successful operation of reverse osmosis in the plant of the municipal waste landfill of lhlenberg (former VEB Deponie Sch6nberg) near the city of Ltibeck in Germany, the most modem and largest multi-stage plant that has been realized up to this time for landfill leachate purification, demonstrates the possibilities of modem membrane technology. Some results are given as example in Table 1. This reverse osmosis system with a capacity of 36 m3/h has been in operation without any problem since the 15th of December of 1989 with one change of the membranes till now. With two reverse osmosis stages, the average rejection rates for salts and organic contaminants are about 99°,6. Depending on the salt content of the feed water and the operation time
T.A. Peters./Desalination 119 (1998) 289-293
between the cleaning cycles, the operating pressure ranges between 36 and 60 bar at ambient temperature. The specific p¢cmeate flux was calculated to be approximately 15 l]m 2 h. Table 1 Typicalplantperformancein leachatepurification Parameter pH-value El. conduct., ~S/em COD, mgO-/l Ammonium, mg/l Chloride,mg/l Sodium, mg/l Heavymetals, mg/l
Ix,achatePermeate 1Permeate2 Rejection, % 7.7 6.8 6.6 17,250 382
20
99.9
1,797
15
<15
>99.2
366
9.8
0.66
99.9
2,830 48.4 1.9 4,180 55.9 2.5 0.25 <0.005 <0.005
99.9 99.9 >98
Similar results are reported from other plants, for example from the landfill Kolenfeld near Hannover, with start up in February 1990. This plant, operated with 1.8 mS/h, has an availability of over 90%. The electric conductivity of the feed is reported to be 15,000 to 16,000 ttS/em, the rejection rate always more than 98%, for COD 99%o. New membranes were installed in April 1993, after more than 3 years in operation because of a decreasing permeate flux. These data from long term experience have also been confirmed by the results of the other more than 120 systems that are in operation on different landfills up to now and by the data collected during numerous tests with pilot plants in technical scale all over Europe, North America and in some countries in Far East. 3. Handling o f ieachate concentrate
The purification of landfill leachate helps to avoid further contamination of the resources like groundwater and surface water. But beside the ecological aspect---the minimization of the burden on the environment~also has to be taken
291
into consideration the commercial feasibility, i.e. the affordability. In this regard membrane filtration has proved to be a justifiable and economic solution in most of the cases, even when the overall costs for the purification are compared with other approaches for the treatment of landfill leachate. This evaluation includes the handling of the concentrate produced in the reverse osmosis plants with 75 to 80% recovery rate, that in the past has been considered to be a very cost intensive step. That applies in fact for few plants in operation, that are using evaporation and drying followed by deposition of the dry residues in a special landfill. However, today other possibilities are gaining importance. They have been developed considering the best technology available and at the same lime ecological and economical requirements. These are: a) transport of the concentrate to an incineration plant equipped for the burning of liquid hazardous waste; b) the solidification of the concentrate with different materials, like fly ash [5] or sludges from waste water treatment plants [6], and disposal of this kind of dry residue on the landfill itself; c) controlled reinjection of the concentrate into changing areas of the landfill in order to improve the biochemical degradation process in the waste itself and accelerate the immobilisation of the organic matter. This solution should be considered as first approach, as a landfill usually can be compared to a bioreaetor that under optimal operating conditions will produce valuable landfall gas, in this case accelerating at the same time the desired imrnobilisation of organic components [7]. If the system for the controlled return of the concentrate to the landfill is designed according to the needs and the respective conditions on site no changes for the concentration of poUutants in the leaehate being pumped from the landfill to the purification plants are to be ex-
292
T.A. Peters ~Desalination 119 (1998) 289-293
peeted. This has been demonstrated on different landfills, in one case since 1986 [1,8,9]. Nevertheless the decision about the concentration factor of a leachate purification system should be based on eval~.~_afioncriteria that include all kind of economical and ecological aspects specific for each landfill site in order to find an op"tmaized solution. In some cases a one stage unit could be sufficient, in others a combination of processes with the highest possible recovery rate should be selected. 4. Volume reduction for the concentrate
Steady improvement of membrane technology has resulted in a high pressure reverse osmosis system based on the DT-module with operation pressures in the range of 120 bar and an adapted process to reduce certain salt fiactions by controlled precipitation. With these developments, the limits for the recovery rate in landfill leachate---given among others by the osmotic pressuro---have been overcome and the concentration factor for the organic and inorganic matter dissolved in the landfill leachate was doubled. This means an increase of the permeate recovery from about 80%--- related to a concentration factor of 5--to 90% recovery with a concentration factor of 10 for the contaminants retained by the membrane. Thus the limit for the electric conductivity in the concentrate of a reverse osmosis plant was increased from 50,000 to 60,000 ~tS/crn to the range of 100,000 to 120,000 ~tS/em [4]. Due to the high volume reduction related to this increase of pure water recovery, this technology allows the need for subsequent evaporation steps to be eliminated. After being processed with high pressure reverse osmosis, the concentrate can then be fed directly into a dryer or a solidification device, or be burned. Such high pressure reverse osmosis systems are in use actually at about 25 plants. On the Ihlenberg landfill site high pressure reverse osmosis has been working since January
1992 with a salt rejection of more than 99%, for example from 73,280 ~tS/cm in the feed to 434 pS/cm in the permeate. The average specific energy demand for this concentrate stage is 14 kWh/m3 permeate, whereas the leachate stage with 80% recovery in fi'ont of this system is consuming less than 5 kWh/m3. The continuous growth of this landfill and the accompanying increase in leachate required the expansion of the purification capacity. On December 17, 1993 the next reverse osmosis plant was brought on line with an integrated high-pressure stage (manufacturer PALL ROCHEM) that increased the input capacity to another 48 m3/h of raw leachate [5], being possible under favourable conditions a permeate recovery up to 90%. 5. Process improvement with nanofiitration
Even better permeate recovery rates can be reached by installing a combination of nanofiltration and fractionated removal of solids together with reverse osmosis and high pressure reverse osmosis. Nanofiltration allows material dissolved in water to be separated into monovalent and bivalent ions. Consequently, the high rejection rate for sulphate ions and for dissolved organic matter together with very low rejection for chloride and sodium reduces the volume of concentrate. Some example for rejection rates for different components dissolved in landfill leachate are shown in Table 2 [10]. For this application, very specific nanofiltration membranes have to be selected and the module must be suitably designed to optimize the interaction of flow parameters such as feed flow velocity, pressure drop, efficient membrane cleaning, insensitivity to micro-particles. Also, a good cost/performance ratio must be achieved. These requirements for successful and continuous separation of heavily loaded waste water are met by the DTF-module, a flat channel module consisting of only a few components in which open-channel construction is combined with narrow gap technique.
T.A. Peters. ~Desalination 119 (1998) 289-293 Table 2 Example for rejection rates for nanofiltration Parameter BODs, mg 02/1 COD, nag 02/1 Ammonia,
Feed 480
Pernm~ 280
P,.ejoction,% 41.62
17000 3350
700 1420
95.88 57.61
31200 12760 2670 1030 10900 6.3 61
2345 17730 187 72.7 5010 6.4 43
92.48 -38.95 93.00 92.94 54.04 -29.5
mg/l Sulphate, mg/l Chloride, mg/l Calcium, mg/l Magnesium, rag/1 Sodium, mg/l pH-value El. conduct., ~tS/em
A system operated with 8.5 kWh/m3 of totally produced permeate with a water recovery rate o f 97% is one example for the extremely low overall power consumption of this hybrid process using reverse osmosis, nanofiltration and fraetionated removal of solids. The fact that a permeate recovery rate o f 95 to 97.5% is operating standard today shows that the combination o f reverse osmosis with nanofiltration and crystalliTation is the basis for a economical process for the purification o f landfill lcachate. Based on the technology explained above, companies have introduced an "own and operate" service, where clients simply pay a price per m 3 of leachate treated without capital risk and with minimal operational involvement. Also it is possible to operate equipment for short term emergency situations, caused by heavy precipitation and capacity bottle-necks.
6. Conclusions
The results obtained during the operation of an increasing number of plants under very different conditions prove that reverse osmosis is a
293
very effective msmtment for the purification o f landfill leachate if all design criteria and requirements specific for landfill leachate have been taken into consideration, and i f an adapted module system as well as correlated technologies are used. This includes high pressure reverse osmosis, with operating pressure up to 120 bar and/or nanofdtration in combination with a controlled crystallization process, that allows permeate recovery rates of more than 95%. The elimination of the negative impact of landfill leachate on the environment can be achieved with membrane filtration due to the dramatic minimization of residual waste to beprocessed or immobilized and due to the high quality of the purified water discharged back to nature. The combination of processes designed for this purpose is one example for a sustainable environmentally friendly development. References [ 1]
W. Dahm J.S. Kollbaeh and J. Gebel, Sickerwass~Roinigung - Stand dcr Tochnik 1993/94 - zxfla?mfligc Entwiddunge~ EF-Verlag fla" Energie- und Umwelttechnik GmbH, Berlin, 1994 [2] AMASA, Archives, Ban:elona, 1998 [3] T. Peters, Water Qualityintemational, 9-10 (1996) 23. [4] T. Peters, Prec., Sardinia 95, 5th International Land-
fill Symposium,~ A , S. Margheritadi Pula- Cagli~Jtaly,.,1995. [5] R.Kenner1L and T. Peters,WLB Wasser, LuRund Boden 1-2 (1995) 24. [6]
M. Raphtel, W. Pohl and T. Peters, Lecture abstracts, ACHEMA 1994, Frankfurt. [7] F. Pohland~ Water Quality International, 9-10 (1996) 18. [8} G. Gross¢ G, DcponiesickorwasseramOocmitung bis zur Direkteinleitung und Totalcntsorgung, TAW, 30./31.01.1990, Ostfildcm. [9] P.L.A. Hcnigin, Prec., Sardinia 95, 5th International Landfill Symposium, CISA, 1995; S. Margherita di Pula - Cagliari, Italy, 1995. [10] R. Rautenbach R. and T. Linn, Entsorgungspraxis, 9 (1995) 44.